def sayhello():
    print('Hello World!')
result = sayhello()
print(result)
print(type(result))

def sayhello2():
    print('Hello World!')
    return None
result = sayhello2()
print(result)
print(type(result))

def check(age):
    if age >= 18:
        return "success"
    else:
        return None
result = check(16)
if not result:
    print("未成年")


name=None